1. Technical Field
The present disclosure relates to a vehicle power transmission system.
2. Description of the Related Art
Some self-propelled vehicles such as motorcycles and four-wheeled drive buggy cars are conventionally provided with a power transmission device to transmit a driving force generated by an engine (motor) to a drive wheel. The power transmission device is a machine that changes the rotational speed of a crankshaft of the engine and transmits it to the drive wheel while connecting to and disconnecting from the crankshaft. The power transmission device mainly includes a clutch and a transmission.
The clutch here is a machine that transmits a rotational driving force of the crankshaft of the engine to the transmission side while connecting to and disconnecting from the crankshaft. Moreover, the transmission is a machine that has a plurality of gear stages with combinations of a plurality of gears, and changes the rotational speed of the crankshaft of the engine by a selected gear stage to transmit the rotational speed to the drive wheel side.
In this case, a clutch is described in, for example, JP-A-2013-137039. The clutch described in this document includes a clutch member (clutch hub) that holds a driven-side clutch plate (clutch plate), and a pressure member (pressure plate). The pressure member is placed facing the clutch member to press a drive-side clutch plate (friction plate). A pressure assist cam is provided on an opposing surface of each of the driven-side clutch plate and the pressure member.
The pressure assist cam is an assist mechanism including a clutch member-side first cam surface (hub-side cam portion) and a pressure-side first cam surface (pressure-side cam portion). The clutch member-side first cam surface and the pressure-side first cam surface each include an inclined surface for generating an assist force that increases a pressing force between the drive-side clutch plate and the driven-side clutch plate when a relative rotation is generated between the clutch member and the pressure member upon the clutch shifting to a state where the driving force of the engine is transmitted. Consequently, in the power transmission device described in JP-A-2013-137039, the assist force by the assist mechanism causes the drive-side clutch plate and the driven-side clutch plate to press each other early to shift the clutch to the state where the driving force is transmitted. Furthermore, vibrations from the engine and the like can be prevented from being transmitted to a clutch lever.